Embodiments herein relate to rectifying antennas (rectennas) for wireless power transfer. Some aspects of the disclosure are directed to broadband antennas (also known as wideband antennas), rectifying circuits or rectifiers, and techniques for eliminating impedance matching networks conventionally connected between the broadband antennas and the rectifiers.
Wireless power transfer (WPT), which converts electromagnetic energy (e.g., microwave, radio frequency (RF), etc.) to direct-current (DC) power, has been widely used in applications such as RF identification (RFID) and microwave energy powered unmanned aerial vehicle (UAVs). In recent years, due to the significant development in wireless communications, (e.g., cellular networks, wireless local area networks, etc.) wireless transmitters are conveying increasing amounts of electromagnetic energy over intervening space to various receivers (e.g., cellular base stations, wireless devices, antennas, etc.). Ambient wireless energy harvesting, which collects energy from electromagnetic waves in the environment, is a favorable technology for supplying continuous power to some self-sustainable standalone platforms (e.g., wireless sensors, smoke alarms, health monitors, etc.). A rectifying antenna (rectenna), which converts RF energy to DC power (RF-to-DC), has been a key solution in both aforementioned technologies.
Conventional single-band rectennas are typically capable of receiving RF power over a narrow frequency band and converting the received narrowband RF power to DC power. The DC power may be used to power devices (e.g., RFID devices, UAVs, etc.). Conventional multi-antenna and/or broadband antenna energy harvesting systems combine the output power from different single-band antennas, each of which have a single operating frequency, an associated impedance matching network and a rectifying circuit. The requirement for the multi-band and broadband rectennas to have a corresponding broadband and multi-band impedance matching networks increase costs and weight, reduce efficiency, and introduce performance variations associated with the complexities of the impedance matching networks.
Moreover, due to a non-linearity of operation of the rectifying circuit, the performance of broadband and multi-band rectennas using complex impedance matching networks is very sensitive to varying operating conditions, such as varying input power levels and varying loads.
A need exists for rectennas comprising simple structures and achieving consistent performance.